Disc drives are used for data storage in modern electronic products ranging from digital cameras to computer systems and networks. Typically, a disc drive includes a mechanical portion, or head disc assembly (HDA), and electronics in the form of a printed circuit board assembly (PCBA), mounted to an outer surface of the HDA. The PCBA controls HDA functions and provides an interface between the disc drive and its host.
Generally, a HDA comprises moving parts such as one or more magnetic discs affixed to a spindle motor assembly for rotation at a constant speed, an actuator assembly supporting an array of read/write heads that traverse generally concentric data tracks radially spaced across the disc surfaces and a voice coil motor (VCM) providing rotational motion to the actuator assembly.
A disc drive unit typically includes a housing that protects the workings of the drive from particulates and other contamination. Control of the internal relative humidity (RH) within the housing of the disc drive is desirable since the moisture content of the surrounding air affects the performance and reliability of the head/disc interface (HDI), a crucial part of the disc drive recording system. For example, it is known that head-to-disc stiction and media corrosion are aggravated by high relative humidity levels. As a further example, excessive disc wear has been observed under conditions of very low relative humidity.
A majority of commercial hard disc drive products incorporate elements that limit the rate of moisture exchange between drive interior and the environment. Such elements include seals, diffusion tubes, carbon absorbers, and desiccants. The effect of these elements is simply to delay changes in relative humidity. They do not control relative humidity levels to a given level, nor do they prevent eventual equilibration over the full range of external (ambient) relative humidity (from 0 to 100%). Commonly used methods to control RH in general commercial applications require costly elements and/or systems (such as sensors, control electronics and software, evaporators, condensers, etc.) that preclude their use in hard disc drives and other such assemblies that include moving parts.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.